1. Field of the Invention
The present invention relates to a surface-coated flame-retardant particle, a flame-retardant resin composition using the same, and methods of producing the same. In particular, the present invention relates to a surface-coated flame-retardant particle and a flame-retardant resin composition using the same that are used for protection, from the troubles by heat such as fire, of various products including frames for consumer electronics and OA products, electric wires and cables, vehicles such as automobile, ship, airplane, and railroad train, building materials, electronic devices and printed board.
2. Description of the Related Art
Halogen compounds, antimony trioxide, phosphorus compounds, hydrated metal compounds (metal hydrates) and the like have been used as flame retardants to be mixed with matrix resins (hereinafter, referred to simply as “resin”) so as to impart flame-retarding property thereto. Among flame retardants, use of halogen compounds and antimony trioxide is declining because of environmental concern, but hydrated metal compounds can reduce the environmental load and are more advantageous also from the viewpoints of resin recycling.
However, the hydrated metal compound has to be used in a large amount in order to provide flame resistance equivalent to that imparted by other organic flame-retardant compounds. Therefore, use of a large amount of the hydrated metal compound results in drastic deterioration of the physical properties of the polymer. In order to impart flame resistance equivalent to that imparted by other organic flame retardants without deterioration of the physical properties of the polymer, it is necessary to disperse hydroxylated metal compound particles with a small diameter in a matrix resin uniformly such that they are separated from each other without aggregation. Thus, when metal hydrate particles are mixed in a resin, it is necessary to form a uniform coating layer on the particle surface, so as to ensure the dispersion state of the particles in the matrix resin.
Surface treatment with a higher fatty acid or the like, formation of a silica layer, and the like are known as methods for forming a coating layer on particle surface (for example in Japanese Patent Application Laid-Open (JP-A) Nos. 52-30262 and 2003-253266, the disclosures of which are incorporated herein by reference). However, when such methods are applied to nanometer-sized particles, the particle in the aggregated state undergoes coating reaction under conventional reaction conditions because the particles are difficult to disperse sufficiently and the coating reaction rate is high; as a result, uniformly coated particles are not obtained.
Further, it has been proposed to treat surface of inorganic powder with a polyamino acid or a gas-phase cyclic organosiloxane (for example in JP-A Nos. 57-145006 and 61-268763, the disclosures of which are incorporated herein by reference). These methods also resulted in insufficient dispersion of the particles and generation of aggregates when applied to nanometer-sized particles.
A method of preparing fine particles enclosed with a linear polymer by mixing and reacting an organic metal complex or the like with the linear polymer in a solvent has been also proposed (for example in JP-A No. 2003-92207, the disclosure of which is incorporated herein by reference). The method provides uniform particles owing to stabilization of the organic metal complex by the linear polymer and owing to controlled reactivity of the organic metal complex. However, the method has a problem that when the reaction proceeds in the three-dimensional supermolecular structure, it is difficult to obtain particles having a uniform particle diameter due to unevenness of the reaction field caused by higher spatial freedom inside the linear polymer network.
Further, polymer nanocomposite compositions of a polyamide and a modified silicate salt, graft polymers, polycarbonate blends containing a phosphonate amine and inorganic nanoparticles, and the like have been also proposed recently for imparting flame-retarding property to resins by using fine particles (for example in Japanese Patent Application National Publication Nos. 2003-517488 and 2003-509523 (corresponding to WO99/041299 and WO01/018117), the disclosures of which are incorporated herein by reference). However, none of these compositions can solve the problems above when used as a flame retardant.